The present invention relates to an optical detection system and, more particularly, to an optical detection system for use in a multi-phase flow combustion system.
There is a recent trend toward improving the operation of industrial process plants in the areas of efficiency, emissions, reliability, and safety. Sensor technology is becoming more important than ever for achievement of success in the above mentioned areas. High quality sensor data obtained from real-time, in-situ, and spatially resolved measurements are critical for on-line or off-line optimization, emissions monitoring, system or component health monitoring, and detecting warning signs of impending catastrophic failures.
A sampling system that performs conventional extractive types of measurements provides quasi in-situ, and spatially resolved data, but cannot provide real-time data due to an inherent delay associated with the sampling system. Furthermore, once a sample gas is extracted, it follows a different flow path and its original properties may be modified. Therefore, for high quality sensor data, a conventional extractive type sampling system is not appropriate and another type of sensor is sought.
For many industrial processes, the multi-phase flow combustion system, a coal-fired furnace for example, presents extremely harsh environments for the application of sensor technology. Very few sensors can survive the high temperature, for example, inside a flame zone of the coal-fired furnace. Those sensors that survive are often either prohibitively expensive, require high maintenance, or have a limited life. For a multi-phase flow combustion system such as the coal-fired furnace, intrusive sensors for in-situ measurements encounter even more challenging problems. Particulates can adhere to surfaces of the sensor and plug up a probe. A reducing or oxidizing environment can also cause unwanted reactions on the surfaces of the sensor leading to sensor failures.
Optical sensors have been employed in non-intrusive gas sensing to avoid the problems mentioned above. Optical sensing techniques generally involve either detection of light emitted from the multi-phase flow or detection of the response of the multi-phase flow as it interacts with an external light source. When employed in a large-scale reaction type multi-phase flow, optical sensors are also susceptible to practical problems. Particles in the multi-phase flow can severely block or scatter light. Broadband absorption by molecules such as H2O can greatly attenuate the light. The limited intensity of the probing light beam may not fully penetrate a multi-phase flow field, particularly if the multi-phase flow field is large, the particulate loading is high, or the concentration of a species capable of broadband absorption is high. Similarly, light emissions from the far side of the line-of-sight may be blocked, scattered, or absorbed before the light emissions can reach the detector. Particles often foul the optical surfaces. Other problems common to multi-phase flow, which is turbulent and has non-uniform thermal and chemical properties, are beam steering and the inability of de-convoluting spatial variations along the line-of-sight.
Sensors are often dedicated to only one type of measurement. Thus, multiple detection systems including different types of sensors are required to meet multiple sensing needs. A cost and complexity of installing multiple detection systems is a hindrance to broad application of multiple detection systems. Sensors that can perform more than one type of measurement are limited, but are definitely attractive in terms of cost and simplicity.
Multiple location sensing is desirable for determining spatial variations, and capturing different phenomena that take place in different locations of the reactive type multi-phase flow. This requires multiple sensors. In some cases, it may even require different kinds of sensors. The cost of the system is usually proportional to the number of sensors installed.
Given the problems discussed above, it is desirable to design components capable of integrating multiple measurement types in one sensor. It is also desirable to provide cost effective methods for sensing at multiple locations of a widely changing operating environment, locations starting from the burners and ending at the exhaust stack.